DESCRIPTION: The assumption on which this application is based is that factors that enhance mammary cell proliferation act to promote the development of breast cancer, and factors that inhibit proliferation serve as anti-promoters. Several dietary factors have been posited to influence mammary epithelial cell proliferation. The overall goals of the proposed study are to identify associations between various dietary factors and proliferation, as demonstrated histologically and by direct tissue assays, in benign fibrocystic breast lesions and in the mammary epithelium adjacent to both benign and malignant breast tumors. There are also plans to compare dietary factors in women with malignant and proliferative benign breast lesions, accounting for histologic evidence of proliferative changes in the surrounding non-tumorous tissue. Study subjects will be selected from among over 267,000 female textile workers in Shanghai, who were enrolled in 1988-89 in a randomized trial of breast self-examination (BSE). Women in this cohort, who, during a 5-year period, develop breast cancer or fibrocystic lesions, and normal age-matched controls selected from the cohort, will be interviewed to obtain information on risk factors for breast cancer, frequency of intake of multiple foods, recent dietary changes and recent intake of phytoestrogen-rich foods. All data will be gathered prior to diagnosis. Blood specimens will be collected and assayed for various lipids, antioxidant vitamins, and isoflavones. Histologic slides from all cases will be collected, the lesions will be classified, and both the benign lesions and normal tissue will be evaluated for various morphologic and immunocytochemical indicators of ductal and lobular proliferation. Unlike prior studies, consumption of foods in this study sample covers a range over which not only breast cancer rates are expected to vary widely, but also phytoestrogen consumption is high, providing an opportunity to evaluate their role in breast cancer. Also unlike prior epidemiologic studies of diet and breast cancer, in the proposed investigation the primary end points are various indices of cell proliferation.